1. Field of the Invention
The present invention relates generally to virtual private networks. More particularly, the present invention relates to methods and apparatus enabling virtual private network based mobile communications.
2. Description of Related Art
Conventional virtual private networks deployed on a public network infrastructure provide clients the same security, management, quality of service policies, and benefits provided to clients in private networks. Typical applications of virtual private networks (VPN) allow remote network nodes such as telecommuters, suppliers, partners, or distant offices access to a private network such as a company network through a VPN server. Many VPN applications use IPsec (Internet Protocol Security) to provide encryption and authentication of messages between a VPN client and a VPN server. The secure connection between a VPN client and a VPN server is often referred to as a VPN tunnel. In most cases, a VPN client accessing a private network through a VPN tunnel can enjoy the same privileges and access capabilities as a client within the private network.
However, conventional virtual private networks have not been designed to allow mobile VPN clients. A VPN client with a particular client IP subnetwork address associated with a particular subnetwork can typically only access the private network through the VPN server as long as the VPN client maintains the same IP subnetwork address. If the IP subnetwork address of the VPN client changes, the sessions the VPN client has with the nodes in the private network are terminated. It should be noted that a client is generally referred to as a VPN client after a VPN tunnel is established. However, a potential VPN client with a VPN tunnel either broken or not established will still be referred to herein as a VPN client for clarity.
More particularly, the IP subnetwork address of the VPN client changes when the VPN client moves from a first subnetwork to a second subnetwork. For example, a laptop user riding on a train may be accessing a private network through a VPN server. The laptop user may be assigned a particular IP subnetwork address associated with a first subnetwork. However, when the vehicle moves into a second subnetwork, a new IP subnetwork address is assigned to the laptop user. The VPN tunnel is not maintained when the IP subnetwork address of the VPN client changes. Thus, after moving to a different subnetwork, the VPN client can only access the private network by establishing a new VPN tunnel to the VPN server. However, establishing a new VPN tunnel disrupts any sessions that the VPN client may have been conducting with network nodes. As a result, this disruption prevents seamless communications between the VPN client and various network nodes when the client moves. Virtual Private Networks are described in more detail in Implementing Virtual Private Networks by Steven Brown (ISBN: 007135185X), the entirety of which is incorporated by reference for all purposes.
Other standards such as MobileIP allow users to maintain existing sessions when moving between various subnetworks. However, many conventional MobileIP standards do not provide for secure connections. Furthermore, not all clients wishing to access a home network securely have Mobile IP. Consequently, it is desirable to provide improved mobility solutions for VPN clients using VPN.